Polyester polymer pellets, and in particular polyethylene terephthalate homopolymers and copolymers (PET), experience a loss of intrinsic viscosity (It.V.) during melt processing in, for example, an injection molding extruder. As a result of losing It.V., the physical properties of the polymer also degrade. One cause of It.V. loss is the hydrolytic degradation of the polymer caused by water absorbed in the polymer prior to melt processing. To prevent hydrolysis, the polymer is thoroughly dried prior to melt processing. While drying the polymer reduces the loss of It.V., nevertheless, some drop in It.V. is experienced, thereby requiring the use of a polymer having an It.V. higher than the target container It.V. to compensate for It.V. losses during extrusion. The use of higher than target It.V. polymers has the added disadvantage of higher costs due to more energy consumption required to heat the polymer for a longer time and to agitate a more viscous material, and/or due to the extension of the residence time during melt phase polymerization to bring the It.V. up to the desired level, resulting in a decreased production rate. The use of higher than target It.V. polyester polymers also has the disadvantage of requiring more energy to feed the polymer along the screw in the extruder.
It would be desirable to reduce the loss in It.V. experienced by the polyester polymer during melt processing for making containers.